a) Field of the Invention
The present invention relates to an oxygen electrode for measuring an oxygen concentration, and more particularly to an oxygen electrode for measuring an oxygen concentration which is suitable for miniaturization and/or easy to use.
b) Description of the Related Art
An oxygen electrode is used in various fields for the measurement of a concentration of oxygen dissolved in liquid. For example, for the purpose of water quality maintenance, biochemical oxygen demand (BOD) of water is measured. The dissolved oxygen concentration can be measured with an oxygen electrode. In the field of fermentation industries, it is desired to regulate the dissolved oxygen concentration in a fermenter in order to efficiently promote fermentation. For the measurement of this dissolved oxygen concentration, an oxygen electrode can be utilized.
If immobilized enzymes are used with an oxygen electrode, a biosensor can be formed. Such a biosensor can be used for the measurement of a concentration of sugar, alcohol, or the like. For example, by using immobilized enzymes such as glucose oxidase with an oxygen electrode, a glucose concentration can he measured. Glucose reacts with dissolved oxygen under the catalyzer of glucose oxidase, and generates gluconolactone. Since the amount of dissolved oxygen diffused in an oxygen electrode cell reduces, the glucose concentration can be measured on the basis of a consumption amount of dissolved oxygen. Oxygen electrodes can be used therefore in various fields such as environment measurements, fermentation industries, and clinical treatments.
In the field of clinical treatments in particular, an oxygen electrode is mounted on a catheter and inserted in a body for measurements. For such applications, it is desired that an oxygen electrode is compact, low cost, and disposable.
Conventional oxygen electrodes have been fabricated on a substrate of glass or vinyl chloride. These oxygen electrodes are difficult to be made compact and are not suitable for mass production. The present inventors have proposed a compact oxygen electrode of a new type which is manufactured by utilizing lithography and anisotropic etching (JP-A-63-238549). This oxygen electrode has a structure with a recess that is formed in a silicon substrate through anisotropic etching, two electrodes with an insulating film interposed therebetween are mounted, electrolyte containing solution is introduced in the recess, and lastly the upper surface of the oxygen electrode is covered with a gas permeable film.
The present inventors have also proposed a technology by which an electrolyte layer and a gas permeable film are formed only at necessary areas by means of screen printing (JP-A-5-87766). This oxygen electrode is compact, has less variation in its characteristics, and can manufacture with low cost because of a capability of mass production. The present inventors have also proposed a compact oxygen electrode more suitable for mass production and with higher quality by using a combination of anisotropic etching and anodic bonding (JP-A-4-125462).
Even with these conventional techniques, it is not easy to manufacture an oxygen electrode suitable for being mounted on a catheter and easy to be inserted in a body. In the field of clinical treatments, it is desired to make an oxygen electrode as small as possible.
In a conventional oxygen electrode, wiring patterns for interconnection between electrodes, lead wires, pads, and the like are juxtaposed parallelly on the same plane. In many cases, this arrangement does not pose practical problems, but spaces required for lead wires and the like cannot be neglected if the oxygen electrode is to be minimized more.
In the case of an oxygen electrode used in contact with liquid, it is almost impossible from the following reason to set the distance between lead wires to about 1 .mu.m as in the case of semiconductor ICs. In an oxygen electrode whose cathode and anode contact electrolyte contained therein, if the distance between lead wires is made too short and if, for example, the gas permeable film is accidentally peeled off, the electrolyte percolates to the lead wire region and allows reaction to proceed. In order to increase product reliability, the wiring patterns including lead wires are required to be spaced apart by 100 to 200 .mu.m or more. However, this space becomes a critical issue if an oxygen electrode having a width of 1 mm or less at the top portion is to be manufactured.
As above, miniaturization of oxygen electrodes are being made. As the oxygen electrode is made more compact, new problems have become conspicuous. As the oxygen electrode is made compact and the width thereof is narrowed, connection to an external circuit becomes difficult. Furthermore, if the substrate is made of fragile silicon or glass, the connection portion of the oxygen electrode to the external circuit becomes likely to be broken by stress during handling it.